Butter and flour an 8 inch round cake pan and a 1.5 quart ovenproof bowl. Make the cake batter, and divide it between the pan and the bowl. Bake at 350 degrees until a toothpick comes out clean, about 35 minutes for the pan, 40 to 45 minutes for the bowl. Let cool, then unmold the cakes onto a rack.

Microwave the white chocolate at 50 percent power in 15 second intervals, stirring, until melted, about 2 minutes. Pour onto a parchment paper lined baking sheet and spread to 1/4 inch thick with an offset spatula. Sprinkle with the sanding sugar. Chill until set, about 10 minutes.

Cover the entire cake with a thin layer of blue frosting (this is called a
crumb coat, which is like a primer. It doesn’t have to be perfect). Chill, uncovered, until the frosting sets, about 15 minutes.

Spread the remaining blue frosting evenly over the cake and doughnuts. Arrange the white chocolate pieces on the igloo in a mosaic pattern. Place the even white chocolate tiles around the tunnel entrance.

For the trees, mix 3/4 cup vanilla frosting with the green food coloring. Spread on the cones, flicking the frosting with the tip of an offset spatula to form branches. Arrange the trees around the igloo and dust with confectioners’ sugar.